Gear type positive displacement pump



Feb. 4, 1958 R. R. ERICK ET AL 2,821,929

GEAR TYPE POSITIVE DISPLACEMENT PUMP Filed June 21, 1954 2 Sheets-Sheet 1 V nm/ INVENTORS Q) E) Ric/MED P. ERICK E JOHN 7? 5351mm: f1? y- 2/ W A 2 ATTORNEY Feb. 4, 1958 R. R. ERICK ET AL 1,

GEAR TYPE POSITIVE DISPLACEMENT PUMP Filed June 21, 1954 2 Sheets-Sheet 2 a 6 M a I IN VENTORJ Elam/PD 7?. E RICK Jomv 77 Ros/Nam BY 2 ATTORNEY United States Pat t GEAR TYPE POSITIVE DISPLACEMENT PUMP Richard R. Erick, South Bend, Ind., and John T. Robinson,

Hamilton, Ohio, assignors to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application June 21, 1954, Serial No. 438,270

4 Claims. (Cl. 103126) causes objectionable noise in the operation of the pump and adversely etfects the mechanical efficiency and life of the pump. Various ways have been proposed for releasing this trapped fluid but all seem to have some objectionable feature such as, for example, requiring the use of complicated valve mechanism, special teeth or expensive and hard to machine passages. Not a few of the attempts at relieving the entrapped fluid have resulted in a loss of volumetric efliciency without having accomplished'the primary objective-of adequately relieving high trapping pressures.

As a corollary of relieving the entrapped fluid there is a problem of relieving the vacuum created in the pocket between the teeth after the fluid has been relieved and before the pocket has been opened by the disengagement of the teeth. This problem is often ignored in the attempt to relieve trapped fluid, yet a complete solution of the problem of trapping fluid requires that provision be made to relieve not only high pressure areas but excessively low pressure areas as well.

It is, therefore, an object of the invention to provide a gear pump having escape means for fluid confined between meshing teeth.

Another object of the invention is to provide a gear pump having means for connecting the suction pocket formed between the disengaging teeth with the pressure pocket formed between engaging teeth.

An additional object of the invention is to provide a trapping relief for a gear type pump having standard gears which is effective irrespective of the direction of rotation of the pump.

A further object of the invention is to provide a gear pump having passages in the side plates thereof for permitting the escape of fluid trapped between the meshing teeth.

Still a further object of the invention is to provide a trapping relief for a gear type pump which is simple in construction, inexpensive to manufacture and which maintains the volumetric efliciency of the pump.

The above and other objects and features of the invention will be apparent from the following description of the device taken in connection with the accompanying drawings in which:

Figure 1 is a plan view, with the cover partly broken away of one form of gear pump incorporating the invention;

Figure 2 is a view taken along line 2--2 of Figure 1; and

Figures 3, 4 and 5 are enlarged views of a portion of Figure 1 showing the teeth in various stages of mesh.

Referring more specifically to the drawings, numeral 14) designates a pump body or housing, 12 a cover mount- 2,821,929 Patented Feb. 4, 1958 'ice ed thereon by bolts 14, .16 an inlet, and 18 an outlet for said body. A driving gear 20 keyed to a shaft 22 is rotatably disposed within the body in meshing relationship tofa gear'24 keyed toa shaft 26 which is carried in the body. A lining member 28 is located in the interior of the pump body, and together with the cover 12 is adaptedto cooperate with the gears 20 and 24 for conveying fluid from the inlet 16 to the outlet 18 where the fluid is put under. pressure. It is to be understood that the driving gear 20 may rotate in either direction with equal facility but for purposes of describing a single embodiment, it is considered to rotate in a counter-. clockwise direction as illustrated in Figure 1 by the direction of the arrow.

.The gears 20 and 24 are of the spur gear type of standard commercial design and are provided with teeth 32 and 34 respectively. These gears have an addendum circle 40, a pitch circle 42 and root circle 44. Teeth 32 and are provided with tips 54 and 56 respectively which have a clearance 58.

Fluid is received at the inlet by the gear teeth and carried to the outlet in a manner familiar to those skilled in the art. -To prevent the entrapment of fluid in pockets 60 and 62 formed between meshing teeth 32 and 34, X- shaped or crossed channels 64 are provided in the lining member 28 and cover 12. It is obvious that if an escape of some kind is not provided for the fluid confined in the pockets 60 and 62, the gear teeth would tend to compress a substantially non-compressible fluid, such as oil, which would result either in pump destruction or excessive bearing loads and attendant vibration, wear, noise and leakage. The center of the X is located at the intersection of the line of centers 66 and the pitch circles 42. The height of the X-shaped slot measured in a transverse direction with respect to the line of centers is limited by the tooth thickness. The width of the X-shaped slot measured along the line of centers must be greater 'than tooth depth measured from root circle to addendum circle. The apexes of the X-shaped slots or channels are designated A, B, Cand D as shown in Figures 1, 3, 4 and 5. With the gears in the position shown in Figure 2, tooth 34a is on the line of centers in fully meshed and engaged position between teeth 32a and 32b, and pocket 60 is at minimum volume. In this position, flow of fluid in or out of pocket 60 through the X-shaped slot 64 is prevented by tooth 34a. counterclockwise rotation of gear 20 to the position shown in Figure 4 moves tooth 34a past the line of centers in a direction to disengage said tooth whereby the volume of pocket 60 is caused to increase. As tooth 34a commences to move in a disengaging direction, tooth 32b engages teeth 34a and 34b forming a pocket 62 therebetween having a volume that is decreasing at the same rate the volume of pocket 60 is increasing. It is apparent that the fluid trapped in pocket 62 would reach an excessively high pressure as the volume of said pocket is decreased if an escape were not provided. Conversely, the increase of volume of pocket 60 would result in an excessively low pressure area being created therein if means were not provided for the admission of fluid thereto. To prevent both or either condition of excessively high pressure or excessively low pressures, the X-shaped slot 64 is so arranged that the slot AC connects pocket 60 and 62 the moment the volumes start to increase and decrease respectively so that the surplus of the one is transferred to make up the deficit of the other. It is to be noted, however, that at no time is there direct communication between the pump inlet 16 and outlet 18 through the X-shaped slot; for as soon as the teeth 34a and 32a disengage opening pocket 60 to the inlet side of the pump, the slot AC is closed by the tooth 32b, as shown in Figure 5.

Additional rotation of the gear 20 in the counter-clock wise direction would create another .pair .oi. pockets iof increasing and decreasing volumes connected by the slot DB. v

It is to be understood that a similarcycle Jot/operations would take placeif the=gear$20were rotatedxin-theopposite or clockwise'zdirection; a :the trappingw relief- -:of our invention being equally effective in either; direction of rotation.

The dimensions of theslots AC tor. DB and the orientation of theslots withrespect-to the intersectionwofthe line of centers' and pitch circles :mayabe varied to. meet the requirements of aparticular device =within ithe? .limitations set out above. Ithas been determined; .however, that I for maximum effectiveness of :the: trapping relief, i; e. the optimum ratio of the'tperiod'iof.fluid 'transfer through the relief. to theperiod when the reliefi is cutoff, is obtained by locating the X-shaped or crossed channe1-64 in the following :mannerz locating'thesintersection .of the line of centers and ipitchqcircles ofthe gears 20 and 24; circumscribing. acircle on the cover. 12. and liner 28 having a center at orcoaxialswith-said intersection and .having a diameter. equal to 1.25. times the tooth thickness; and forming a pair ofcrossed channels -centered with. respect to said.circle and extending radially to the circumference thereof.

It should :be emphasized that awgear pumpJincorporating the. features of this invention has :a relatively higher efiiciency and .is subject to.-less..wear and leakage than pumps utilizingbacklashor escape passages-to thesuction or discharge portions of'the pump.

Although the invention. has. :been described in connection with one specific embodiment,.the principles are susceptible of numerous .OthEILflPPliCQfiQHS that will readily occur to persons skilledin the art.

We claim:

1. In a ,fluid pump or motor, ahousing-having an inlet and an outlet, a pair :of gears arranged in meshing relationship with theteethin mesh forming two pocketstherebetween in which fluid is entrapped, a channel-formed in the sidewall of said housingin registration with said pockets, said channel symmetrically .centeredat-the intersection of the line of-centers and .the pitch. circles of said gears and extending .in a-.direction.paralle1 to the lineofcenters. a. distance greaterthanthe total tooth depth and in a direction transverse thereto a distance not exceeding tooth thickness.

2. In a fluid pump or motor, a housing, driving and driven gears arranged in meshing relationship with pockets formed between the teeth .in mesh, crossed channels formed in the side wall of said housing in registration withtsaid pockets,..said crossed channels being symmetrically centered at the intersection of the line of centers and the pitch circles of said gears and extending transverse the line of centers a distance not exceeding tooth thickness.

3. In afluid pump or motor, a housing, a pair of gears arranged in meshing relationship with pockets formed between the teeth in mesh, and crossed channels formed in said housing in registration with said pockets, each of said channels having a length equal to 1.25 times the tooththickness-of said gears, said channels having an axis -.of symmetry on. the line .of centers of saidgears.

4. In a fluid pump or motor, a housing having an inlet and an outlet, 21 pair of gears .in said housing arranged in meshing relationship with the teeth in mesh forming pocketsof alternately decreasing and increasing volume, crossed .channels in said housing centered at the intersection ofzthe lines of centers and the pitch circles of said gears, the ends of said'channels being in registration with said 'pockets and. the .IeHgthOflSHld channels being equal to .1.25:times' the tooth thickness of said gears.

References Cited in the file of this patent UNITED STATES PATENTS 1,348,773 Auger Aug. 3, 1920 1,686,867 Kuhn Oct. 9, 1928 1,719,025 .Scheminger, Jr. July 2, 1929 1,909,418 Norwood May 16, 1933 2,188,848 .Svenson Jan. 30, 1940 2,281,767 Heckert May 5, 1942 2,344,628 :Monahan Mar. 21, 1944 2,498,790 -Caughrean Feb. 28, 1950 2,601,003 Pontius June 17, 1952 2,601,004 Cintron June 17, 1952 2,604,051 Johnson July 22, .1952 

